1. Field of the Invention
The present invention relates to a power output apparatus configured to output power to a driveshaft and to a hybrid vehicle equipped with such a power output apparatus.
2. Description of the Prior Art
One proposed structure of the power output apparatus includes an internal combustion engine, two motors, a Ravigneaux planetary gear mechanism, and a parallel shaft-type transmission arranged to selectively link an output member with one of two output elements of the planetary gear mechanism respectively connected to the motors (see, for example, Japanese Patent Laid-Open No. 2005-155891). Another proposed structure of the power output apparatus includes a planetary gear mechanism having an input element connected to an internal combustion engine and two output elements respectively connected to motors, and a parallel shaft-type transmission including two countershafts respectively connected to the corresponding output elements of the planetary gear mechanism and linked with an output shaft (see, for example, Japanese Patent Laid-Open No. 2003-106389). In these prior art power output apparatuses, the parallel shaft-type transmission switches over the output element of the planetary gear mechanism to be linked with the output member or with the output shaft.
Because of the limited space for mounting the power output apparatus, there is a difficulty in application of the power output apparatus in the former cited reference to a vehicle having a rear wheel-drive system as a main drive system, that is, a rear wheel-drive vehicle or a rear wheel drive-based four wheel drive vehicle. The power output apparatus in the latter cited reference is applicable to the rear wheel-drive vehicle. The parallel shaft-type transmission, however, has rather large dimensions both in an axial direction and in a radial direction and is thus not suitable for mounting on the vehicle. The power output apparatus in the latter cited reference also requires a rotor of a large diameter and thereby causes its electrical drive system to be rather bulky and unsuitable for mounting on the vehicle. Moreover the power output apparatus in the latter cited reference has the low possibility for the practical application. In application of the power output apparatus in the latter cited reference to the vehicle having the rear wheel-drive system as the main drive system, a further improvement of the power transmission efficiency is required in a wider drive range. There is thus still room for improvement in the power output apparatuses of these prior art structures.